The propagation of guided acoustic waves, such as Stoneley waves and pressure waves in structures, such as pipes or other conduits, is known. In the field of hydrocarbon production, guided acoustic waves have been used for acoustic logging. In accordance with one implementation of acoustic logging, an acoustic tool having an acoustic source and one or more acoustic receivers (e.g., hydrophones) is lowered into the borehole. At each depth, the source emits acoustic waves, usually over a range of carrier frequencies. The time of arrival of these waves at the receivers is interpreted to provide information about the formation surrounding the borehole. This may be accomplished, for example, by examining the propagation velocity of the acoustic waves and the manner in which that velocity varies with the carrier frequency. The attenuation of the acoustic waves may also be considered, again as a function of frequency. While this technique may provide a host of information regarding the formation, it is an intrusive and extremely time-consuming technique.
Another type of measurement that has been conducted with guided acoustic waves in the field of hydrocarbon production involves launching pressure pulses from the surface into the wellbore and observing the time-dependence of the returned acoustic energy. While this technique can provide information about average acoustic velocity or the location of obstructions in the well (e.g., the position of a cement plug or the state of a valve), it requires prior knowledge regarding the properties of the fluid in the well and/or calibration of the wave velocity for the conversion of reflection time to distance along the wellbore.